A boundary element method for modelling piezoelectric transducer based structural health monitoring

In this thesis, several numerical approaches for the development of structural health monitoring (SHM) methodologies for engineering structures are described. In particular, the first boundary element models of three-dimensional piezoelectric smart structures are introduced. Comparing to the finite element method (FEM), the boundary element method (BEM) demonstrates higher numerical stability and requires less computational resources. Also, the dual boundary integral formulation provides a natural and efficient approach for replicating the targets of SHM techniques – material discontinuities. A boundary element formulation for the ultrasonic guided wave based damage detection strategy is firstly presented. The semi-analytical finite element model of piezoelectric patches is coupled with the boundary element model of substrates via the variables of the BEM. The first systematic approach for determining the number of Laplace terms to be used for an elastodynamic boundary element analysis is also introduced. The above-mentioned formulation is then transformed to the Fourier domain for simulating the electro-mechanical impedance (EMI) based damage detection strategy. The key to attaining accurate EMI signatures is the inclusion of appropriate damping effects. In addition to the detection of the damages in substrates, a partially debonded coupling condition between substrates and piezoelectric patches is derived for modelling the diagnosis of faulty transducers. The computational efficiency of the BEM is further enhanced by the implementation of high-order spectral elements. The difficulties associated with the applications of these elements in the BEM are among the key emphases. The accelerated BEM is used to reformat the models of the two damage detection strategies. The performances of the two strategies are more deeply investigated and understood. At the end of this thesis, a technique for the characterisation of cracks in plate structures is established. By utilising a two-stage approach, the long-existed difficulty of the simultaneous localisation and sizing of arbitrary cracks can be overcome. The technique is developed mathematically using analytic models and the FEM, and is extensively assessed by numerically simulated extreme scenarios. Throughout this thesis, physical experiments are heavily relied on for validation studies. A summary of the skills and the experiences, which the author has gained on experimental testing, is reported in this thesis for further reference.Open Acces

Polysaccharide-based aerogels for thermal insulation and superinsulation: An overview

International audienc

Monitoringof CorrosionProcesseswithUltrasound

The consequences of corrosion can be both expensive and dangerous. In the USA alone, corrosion has been estimated to cost the petroleum industry around $8 billion a year. Corrosion damages to pressurized components, such as pipes and boilers, can lead to sudden failures, fatalities and environmental catastrophes. Ultrasonic wall thickness measurement is one of the most used field-deployable techniques for assessing and surveying the effects of corrosion. However, the manual setup and operation of ultrasonic testing equipment often results in poor wall thickness measurement repeatability (~ 0.1 - 0.5 mm). These errors are mainly due to surface preparation, and positioning and coupling errors that are associated with the manual setup of the measurement. It has been demonstrated that the repeatability of ultrasonic inspection can be improved significantly by the use of permanently installed transducers [1]. Measurement precision in the micro-meter range has been achieved for wall thickness monitoring [2, 3]. While it is very difficult to avoid corrosion altogether, industry is interested in detecting corrosion rates that are larger than ~ 0.1 mm/year so that corrosion mitigation strategies for maximizing plant life can be effectively put in place. With manual measurements the corrosion rates of interest can only be detected over time frames that span years. Ultrasonic monitoring with a repeatability of the order of micro-meters means that corrosion rates of industrial interest (i.e. 0.1 mm/year or 270 nm/day) can be detected over a time frame of several days or even weeks. In this paper, an optimized wall thickness monitoring setup with a wall thickness measurement repeatability of 40 nm will be introduced. This enables the detection of the abovementioned corrosion rates over the periods of hours rather than days or weeks. The ultrasonic measurements presented in this paper have been verified by the results of an optical technique and, where possible, by analytic models. The effects of signal-to-noise ratio and temperature variation will be discussed in detail.</p

Tailoring the morphology and properties of starch aerogels and cryogels via starch source and process parameter

International audienc

3-D Modeling of Thermal Exchange in the PV Module During Lamination: Impact of Architecture, Laminator Configuration, and Lamination Recipe

International audienc

High-precision in situ 3D ultrasonic imaging of localized corrosion-induced material morphological changes

Abstract We present an ultrasonic research technique that can carry out in situ, direct monitoring of the 3D morphologies of corrosion substrates. The technique has a customizable lateral resolution, an ultra-high axial resolution of 100 nm, and an experimentally proven measurement accuracy. In using the technique to monitor the localized corrosion processes of carbon steel under constant DCs, it was observed that during each of the experiments conducted in alkaline environments, iron dissolution accelerated for a certain period of time and then slowed down. Based on the various features of the ultrasonic signals acquired and the XRD spectra of the corrosion products obtained, it was deduced that an increase in iron dissolution rate as such was accompanied by the depositing of solid corrosion products onto the substrate used and driven by the formation of Fe3O4, which consumed electrons. After a while, the corrosion product layer collapsed and the formation of Fe3O4 was halted